1. Field of the Invention
The present invention relates to an image sensor and to a method of fabricating the same, and more particularly, to an image sensor for reducing pixel-to-pixel crosstalk and a method of fabricating the same.
2. Description of the Related Art
An image sensor converts optical information into electrical signals. Recently, with the expansion of the computer and communication industries, there has also been an increasing demand for highly-efficient image sensors in various fields such as digital cameras, camcorders, personal communication systems, game devices, surveillance cameras, micro-cameras for medical use, robots, and so on.
A unit pixel in an image sensor converts incident light into an electrical signal, and integrates charges corresponding to the amount of light at a photoelectric converter. In addition, a unit pixel of an image sensor reproduces an image signal through a readout operation. However, the incident light may form charges that are not integrated at the photoelectric converter of the unit pixel. For example, in a charge coupled device (CCD), charges generated in lower and side portions of a photodiode may be injected into a vertical transmission CCD channel, causing what is known as a smear effect. In addition, in a CMOS image sensor, charges may be moved to and integrated at a photoelectric converter of an adjacent pixel, causing what is known as pixel-to-pixel crosstalk.
Referring to FIG. 1, pixel-to-pixel crosstalk may be divided into the following categories: (a) optical crosstalk A which occurs when a reflected light 6 and a refractive light are transmitted to a photoelectric converter 2 of a unit pixel adjacent to a relevant unit pixel, a reflected light 6 being formed by reflection on the top or side of metal wirings M1, M2, and M3, a refractive light being formed by refraction at a non-uniform layer or at a multilayer structure including interlayer insulating layers having different refractive indexes; and (b) electrical crosstalk B occurring when charges generated at the lower or side portion of the photoelectric converter 2 of the relevant unit pixel are delivered to the photoelectric converter 2 of an adjacent unit pixel via a long-wavelength incident light 7.
When crosstalk occurs, resolution decreases in a black and white image sensor, causing distortion in an image. In addition, in a color image sensor using an RGB color filter array (CFA), the probability of crosstalk occurring due to red light having a long wavelength is high, which may cause poor tint. Moreover, crosstalk may cause a blooming effect in which adjacent pixels blur on an image.
Thus, there is a need for an improved image sensor having reduced pixel-to-pixel crosstalk and for a method of fabricating the same.